At present, boron neutron capture therapy (BNCT) is receiving attention as a technology that can selectively kill and treat cancer cells. BNCT requires use of thermal neutrons or epithermal neutrons, thus imposing many constraints such as the necessity for patients to go to a nuclear reactor by which neutrons can be generated and used. Therefore, a small-sized neutron generator that allows generation of neutrons in a hospital has been desired. In a neutron generator, a beryllium or lithium target is bombarded with protons or deuterons accelerated by an accelerator.
As a conventional accelerator, the one as described in Non Patent Literature 1 is known. This accelerator includes an electron cyclotron resonance (ECR) ion source, a radio-frequency quadrupole (RFQ) linac, and a drift tube linac (DTL), which are installed consecutively. In this accelerator, the RFQ linac accelerates deuterons to 5 MeV, and the DTL accelerates them to 40 MeV. A beam of the accelerated deuterons is emitted to liquid lithium flowing over a curved back wall, generating neutrons behind it.